Magnetic field-induced soft mode in spin-gapped high-Tc superconductors

TL;DR

This paper explains the magnetic field-induced softening of spin modes in high-Tc superconductor LSCO through a phenomenological model involving vortex pinning and stripe fluctuations, matching experimental observations.

Contribution

It introduces a model linking vortex pinning to softening of spin modes, providing a new explanation for in-gap spin excitations in high-Tc superconductors.

Findings

Spin gap vanishes around 7T, consistent with experiments.

Vortex regions overlap at critical field, causing mode softening.

Model reproduces observed magnetic field effects on spin excitations.

Abstract

We present an explanation of the dynamical in-gap spin mode in LSCO induced by an applied magnetic field H as recently observed by J. Chang et al. Our model consists of a phenomenological spin-only Hamiltonian, and the softening of the spin mode is caused by vortex pinning of dynamical stripe fluctuations which we model by a local ordering of the exchange interactions. The spin gap vanishes experimentally around H=7T which in our scenario corresponds to the field required for overlapping vortex regions.